4L60E problem
 

My friend posted this earlier but i havent had any luck getting answers so ill post it for my self all information at once so maybe i can get some quick answers b/c this is very anoying!

Anyways... here goes! I have a 96 firebird V6 with an auto trans... the car will act fine for the 1st couple of times through the gears, but then will go into what im told is "LIMP MODE" where the computer wont let the trans get out of 3rd or 4th. With the sugestions of the tranny people i have had the car scanned and the codes are:

OBD-II
P1810 - TFP Valve Position Switch Circuit
P1860 - TCC PWM Solenoid Circuit Electrical
P1886 - Shift Timing Solenoid

Ive talked to the trans people and they tell me that they want to pull it in for their "diagnostics" and charge me like 300 bucks... so i figured if it is somthing electrical (which it kinda sounds like it to me) or somthing not too invasive then maybe i can get the part (found the shift solenoid for 32.00 at orielies) and replace it myself...

So my question is... does this sound like i just need to replace the shift solenoid... and if it is.. where the hell is it located and how do i get to it?

PLEASE HELP ASAP!